feat(adr-185): P4 benchmarks, examples, and README extras for the SOTA wheels

ADR-185 §4.2 pytest-benchmark micro-benchmarks + runnable examples +
README extras table for the aether/meridian/mat bindings.

- python/bench/test_bench_{aether,meridian,mat}.py — follow the existing
  test_bench_vitals.py pattern (skipped by default; --benchmark-only).
- python/examples/{reid_from_csi,cross_room_calibrate,mat_triage}.py —
  typed, runnable, mypy --strict clean.
- python/README.md — SOTA extras table + example links.

Measured on a RELEASE wheel (maturin develop --release --features sota),
reference machine per ADR-117 §10:
  AETHER embed()          mean ~150 us/window   (target <2 ms)   PASS
    batch scaling 1/8/64: 140 / 1091 / 8509 us  (linear, no O(n^2)) PASS
  MERIDIAN normalize()    mean ~2.2 us/frame     (target <200 us) PASS
  MERIDIAN encode()       mean ~6.9 us           (target <200 us) PASS
  MAT ingest+scan_once()  mean ~40 ms/256-frame  (< 500 ms interval) PASS

Acceptance self-verification (ADR-185 §6), all run just now:
  §6.1 default wheel 279 KB (<=5 MB); build_features has no p6-* feature  PASS
  §6.2 pytest tests/test_aether.py    9/9   PASS
  §6.3 pytest tests/test_meridian.py  13/13 PASS
  §6.4 pytest tests/test_mat.py       7/7   PASS
  §6.5 benchmarks meet all targets (above)                                PASS
  §6.6 parity harness: 3/3 SHA golden gates green (cargo test --features
       sota, 6/6); CI *wiring* as a release gate is out of python/ scope  PARTIAL
  §6.7 SOTA accuracy bars on labeled fixtures: NOT met (no labeled
       fixtures / trained models available; parity proves path-equality,
       not accuracy)                                                       OPEN
  §6.8 .pyi stubs present for all three; mypy --strict on the 3 examples   PASS
  §6.9 base wheel `import wifi_densepose.{aether,meridian,mat}` raises a
       clear ImportError naming the extra                                  PASS
  No regression: 76 pre-existing tests pass on the default wheel.

Status NOT flipped to Accepted: §6.7 (accuracy bars) is unmet, §6.6 CI
wiring is pending, and the per-extra wheel-size hoists (sensing-server /
train / mat leaf crates) remain follow-ups. docs/adr/ is owned by another
agent this session, so the ADR ledger edit is deferred to that owner.

python/bench/test_bench_mat.py

@@ -0,0 +1,44 @@
+"""ADR-185 §4.2 — MAT scan micro-benchmark.
+
+Measures the cost of one full ingest + `scan_once()` cycle over the
+committed 256-frame CSI stream. The per-cycle cost should stay comfortably
+below the configured scan interval (default 500 ms) so the binding is not
+the bottleneck.
+
+Run with:
+    pytest python/bench/test_bench_mat.py --benchmark-only
+
+Validated on a RELEASE wheel; a debug wheel will be several× slower.
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+from wifi_densepose import mat
+
+_FIXTURE = Path(__file__).resolve().parents[1] / "tests" / "golden" / "mat_input.json"
+
+
+def _stream() -> list[dict]:
+    return json.loads(_FIXTURE.read_text())["stream"]
+
+
+def test_scan_cycle_cost(benchmark) -> None:
+    stream = _stream()
+
+    def _run() -> int:
+        cfg = mat.DisasterConfig(
+            mat.DisasterType.Earthquake, sensitivity=0.9, confidence_threshold=0.1
+        )
+        resp = mat.DisasterResponse(cfg)
+        resp.initialize_event(0.0, 0.0, "bench")
+        resp.add_zone(mat.ScanZone.rectangle("Zone A", 0.0, 0.0, 50.0, 30.0))
+        for frame in stream:
+            resp.push_csi_data(frame["amplitude"], frame["phase"])
+        resp.scan_once()
+        return len(resp.survivors())
+
+    survivors = benchmark(_run)
+    assert survivors == 1